Method of fabricating a plastic substrate

ABSTRACT

Disclosed is a method of fabricating a transparent plastic display substrate having a barrier layer enabling to prevent the penetration of oxygen and moisture without causing damage on a substrate by annealing a surface of the barrier layer locally. The present invention includes the steps of forming a silicon based barrier layer on a transparent plastic substrate and annealing the barrier layer locally.

TECHNICAL FIELD

The present invention relates to a fabrication of a plastic displaysubstrate having a barrier characteristic against oxygen and moisture,and more particularly, to a method of fabricating a plastic displaysubstrate having a ultra-thin barrier layer which prevents penetrationof oxygen and moisture by forming a barrier layer for securingreliability of a display device and by carrying out thermal treatment ona surface of the barrier layer.

BACKGROUND ART

Demands of various information oriented society due is to developmentsof information communication technology increase the demand onelectronic displays. And, the demanded displays are diversified intoportable devices such as a mobile phone, PDA, notebook computer, and thelike as well as a monitor, TV, etc. When the electronic display devicesare fabricated on substrates according to application of the variouskinds of the devices, such characteristics as large size, low productcost, high performance, thin thickness and the like are required for thesubstrates.

There are various kinds of substrates which are currently used such as atransparent glass or quartz substrate, a transparent plastic substrate,a silicon wafer substrate, a sapphire substrate, and the like. Theglass, quartz, silicon wafer, and sapphire substrates in thosesubstrates have widely been used owing to the previously establishedprocesses and apparatuses. Yet, a great deal of attention is paid to aplastic substrate which is hardly breakable, conveniently portable,light, and flexible as well as easily manufactured.

Compared to the previous substrates such as the fragile glass substrate,a plastic display substrate is hardly breakable and much lighter. Yet,the plastic display substrate itself has the problem that moisture oroxygen in the air easily penetrates into the substrate. Specifically, inorder to be used as a substrate of a display device vulnerable tomoisture or oxygen, fabrication of a substrate free from the penetrationof moisture or oxygen in the air is the major problem to be settled.

In accordance with the research materials read by Ernst Lueder inStuttgart University, Germany at IDW (international display workshop)1999, moisture permeability and oxygen permeability, which are requiredfor using a plastic substrate for a display device, for LCD shouldsatisfy 0.1 g/m²·day (moisture) and 0.1 cc/m²·day (oxygen),respectively. Moreover, in case of an organic electroluminescent displaydevice including a light-emitting material specifically vulnerable tomoisture, 10⁻⁴˜10⁻⁶ g/m²·day (moisture) of the moisture permeability and10 ⁻⁴˜10⁻⁶ cc/m²·day (oxygen) of the oxygen permeability, which arepretty low, are required.

In order to overcome the above problem, many efforts are made to studyvarious methods for forming a barrier layer, which enables to preventthe penetration of oxygen and moisture, on a plastic substrate. And,material fields in the research approach are mainly classified intothree categories including a first case of using a polymer material, asecond case of using an inorganic material, and a third case of usingboth of the polymer and inorganic materials by blending.

Meanwhile, when the barrier layer is formed of a single layer of asingle kind, it is unable to satisfy the barrier characteristic againstmoisture or oxygen. Hence, many efforts are made to study a method ofusing multi-layered barrier layers or a method of forming a barrierlayer including multi-layers by alternating polymer and inorganicmaterials. In U.S. Pat. No. 6,106,933 paying attention to the fact thatpolarity of moisture or oxygen is relatively big, a polyethylene filmhaving hydrophobic property opposite to that of moisture or oxygen islaminated on a surface of a plastic substrate to form a barrier layer.Yet, the corresponding result for moisture is <1.5 g/m²·day and that foroxygen is <45 cc/m²·day. And, both of the results greatly fail to meetthe requirements for an organic electroluminescent display device suchas 10⁻⁴˜10⁻⁶ g/m²·day (moisture) and 10⁻⁴˜10⁻⁶ cc/m²·day (oxygen).Therefore, modification is greatly needed to form a barrier layer havinga hydrophobic polymer material laminated on a plastic substrate to beused as a substrate for an organic electroluminescent display device.

On the other hand, in case of a hybrid type having polymer and inorganicmaterial blended with each other, as taught in U.S. Pat. No. 5,441,816,U.S. Pat. No. 5,415,921, U.S. Pat. No. 5,426,131, or the like, a film isprepared to prevent penetration of moisture and oxygen by blending amaterial selected from the group consisting of polyvinylchloride, tinstabilizer, calcium stearate, butylacrylate rubber graft copolymer, andthe like with TiO₂, coating the blended materials thereon, and hardeningthe coated materials by UV rays.

Besides, in case of using an inorganic substance only as a material of abarrier layer according to U.S. Pat. No. 5,508,075, U.S. Pat. No.5,532,063, IDW'99 (by Ernst Lueder, pp215˜pp218), 11^(th) FPDmanufacturing conference, E1 section (pp17, Tokyo, Japan), etc., asilicon based insulating material such as SiO₂, SiN_(x) (or Si₃N₄),Si+SiO₂, and SiO_(x)N_(y) or Ta₂O₅ is used as the material. In thiscase, a single-layered material is used or two kinds of the materialsare stacked alternately to be used. Specifically, in 11^(th) FPDmanufacturing conference, E1 section, pp17, Tokyo, Japan, a SiO_(x)N_(y)layer is formed 100˜200 nm thick by sputtering as a barrier layer. Thebest moisture permeability of the layers is <1.5 g/m²·day which fails tomeet the requirement of 10⁻⁴˜10⁻⁶ g/m²·day (moisture) sufficiently,whereby modification is needed.

Finally, in accordance with U.S. Pat. No. 5,487,940, U.S. Pat. No.5,593,794, U.S. Pat. No. 5,607,789, and U.S. Pat. No. 5,725,909, amethod of forming a barrier layer on a plastic substrate enabling toprevent the penetration of oxygen and moisture includes the steps offorming a barrier layer of one layer using an inorganic or polymermaterial and forming another barrier layer using an inorganic or polymermaterial alternately. Specifically, the method includes the steps offorming a polymer (or inorganic) layer, forming an inorganic (orpolymer) layer on the polymer layer, and repeating the previous stepsseveral times to form a barrier layer of multi-layers. In this case, thepolymer layer is formed by liquid phase printing, dipping, orpolymerization by depositing monomers of polymer selected from the groupconsisting of cross-linked acrylate polymer, polyvinylalcoholcross-linked with aldehyde, polyfluorocarbon polymer, etc.

In case of forming a barrier layer with 0.04 mil cross-linkedpolyvinylalcohol on a polypropylene film according to U.S. Pat. No.5,487,940, permeability (0.02 cc/100 in²·day) that oxygen penetrates thesubstrate is reduced 30 times less than that (>150 cc/100 in²·day) ofthe case without forming the barrier layer. Moreover, the inorganicmaterial used as a barrier layer material is selected from the groupconsisting of SiO₂, Al₂O₃, SiN_(x), metal such as Al and the like, glassmixture (SnO:SnF₂:PbO:P₂O₅=32:3:8:23), etc. Specifically, in case offorming at least three alternating barrier layers using fluorocarbonpolymer having a hydrophobic property as a polymer material and SiN_(x)or SiO₂ as an inorganic material according to U.S. Pat. No. 5,593,794,(polymer/SiN_(x))×3 shows <8/100 in²·day but (polymer/SiO₂)×3 does<240/100 in²·day. Hence, SiN_(x) has a moisture-penetration preventingcharacteristic which is about 30 times superior to that of SiO₂.Compared to the case of forming the barrier layer using the hybrid layeror the polymer or inorganic layer only, the case of using suchmulti-layers has excellent characteristics relatively but needs to forma plurality of layers using inorganic and polymer materials alternatelyto increase product cost due to the elongated forming time.

Hence, in order to apply the case to the practical mass production, ascheme of reducing the forming time remarkably or bringing a maximumeffect with a minimum layer is required.

As mentioned in the above explanation, only the case of stacking thebarrier layers by repeating the respective layers at least three timesalternately using the polymer and inorganic layers (specially, metal orsilicon based insulating materials) results in the excellent penetrationpreventing characteristics against moisture and oxygen. The more thelayers are stacked, the more the penetration preventing characteristicsincrease. Yet, the forming time is elongated to increase the productcost as well.

Unfortunately, the plastic substrate having the barrier layer accordingto the related art has the following problems.

In order to cut off moisture or oxygen penetrating through a plasticsubstrate completely, stacking resin and inorganic layers should berepeated at least three times. Specifically, it is insufficient toattain the demanded moisture permeability unless the metal component isused as the inorganic layer. Since the substrate should be transparentto be used for a display substrate, this method cannot be applied to thefabrication of the plastic substrate. Moreover, in order to form thebarrier layer of the multi-stacked structure, the process timeincreases, the process becomes complicated, and the product costincreases.

DISCLOSURE OF THE INVENTION

Accordingly, the present invention is directed to a method offabricating a plastic substrate that substantially obviates one or moreof the problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide a method of fabricatinga transparent plastic display substrate having a barrier layer enablingto prevent the penetration of oxygen and moisture with small thicknesswithout causing damage on a substrate by forming a barrier layer of asilicon based insulating material and carrying out thermal treatment ona surface of the barrier layer locally in fabricating a plasticsubstrate applicable to an organic electroluminescent display device.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims thereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a method offabricating a plastic display substrate according to the presentinvention includes the steps of forming a silicon based barrier layer ona transparent plastic substrate and annealing the barrier layer locally.

Preferably, a desiccant layer is inserted between the transparentplastic substrate and the barrier layer.

More preferably, the desiccant layer is selected from the groupconsisting of Al₂O₃, CaO, Y₂O₃, MgO, and polyurea.

Preferably, the barrier layer is selected from the group consisting ofSiO_(x)N_(y) and SiN_(x) or the barrier layer is formed of at least twocomplex layers.

Preferably, the barrier layer is annealed using one of a pulse excimerlaser, a continuous wave oscillation excimer laser, a pulse solid laser,and a continuous wave oscillation solid laser, an annealing powerthereof is 10˜2,000 mJ/cm², and an ambient temperature is below 300° C.

Preferably, the barrier layer is formed by at least one annealing usingone of Ar₂, Kr₂, Xe₂, ArF, KrF, XeCl, and F₂ excimer lasers.

Preferably, the barrier layer is formed to have a stacked structure ofthree layers comprising a silicon based insulating inorganic material,resin, and another silicon based insulating inorganic material.

Preferably, the barrier layer is formed to have a plurality of stackedstructures each of which comprises three layers having a resin layer, asilicon based insulating inorganic material, and another resin layer.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, a method of fabricating a plasticdisplay substrate includes the steps of forming a first silicon basedbarrier layer on a transparent plastic substrate, forming a desiccantlayer on the first barrier layer, forming a second barrier layer on thedesiccant layer, and annealing the first or/and second barrier layerlocally.

Preferably, the desiccant layer is selected from the group consisting ofAl₂O₃, CaO, Y₂O₃, MgO, and polyurea.

Preferably, the barrier layer is selected from the group consisting ofSiO_(x)N_(y) and SiN_(x) or the barrier layer is formed of at least twocomplex layers.

Preferably, the barrier layer is annealed using one of a pulse excimerlaser, a continuous wave oscillation excimer laser, a pulse solid laser,and a continuous wave oscillation solid laser, an annealing powerthereof is 10˜2,000 mJ/cm², and an ambient temperature is below 300° C.

Preferably, the barrier layer is formed by at least one annealing usingone of Ar₂, Kr₂, Xe₂, ArF, KrF, XeCl, and F₂ excimer lasers.

Preferably, the barrier layer is formed to have a stacked structure ofthree layers comprising a silicon based insulating inorganic material,resin, and another silicon based insulating inorganic material.

Preferably, the barrier layer is formed to have a plurality of stackedstructures each of which comprises three layers having a resin layer, asilicon based insulating inorganic material, and another resin layer.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 illustrates a cross-sectional view of a plastic display substrateaccording to the present invention;

FIG. 2 illustrates a schematic diagram of a laser annealing deviceaccording to the present invention;

FIG. 3 illustrates a cross-sectional view of a plastic display substrateaccording to a first embodiment of the present invention;

FIG. 4 illustrates a cross-sectional view of a plastic display substrateaccording to a second embodiment of the present invention; and

FIG. 5 illustrates a diagram of a bonding structure of a silicon nitridelayer as a barrier layer using a silicon based insulating material.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

FIG. 1 illustrates a cross-sectional view of a plastic display substrateaccording to the present invention.

Referring to FIG. 1 a, a thin barrier layer 30 of a silicon basedinsulating material enabling to prevent penetration of external oxygenor moisture is formed on a transparent plastic substrate 20. The barrierlayer 30 includes a single layer or plural layers selected from thegroup consisting of a silicon oxynitride layer (SiO_(x)N_(y)) and asilicon nitride layer (Si₃N₄ or SiN_(x)), and is formed to an initialthickness d1 of 100˜110,000 Å, and more preferably, to 100˜3,000 Å. Thebarrier layer 30 is formed by chemical vapor deposition, sputtering,electron beam, or the like.

When the barrier layer 30 is formed by chemical vapor deposition withthe silicon based insulating material, a deposition temperature of layeris 25˜300° C., an inert gas is used as a carrier gas, SiN_(x) uses SiH₄,NH₃, and N₂ as reactive gases, and SiO_(x)N_(y) uses SiH₄, N₂O, NH₃, andN₂ as reactive gases. When the barrier layer 30 is formed with a siliconbased insulating material by sputtering, a deposition temperature oflayer is 25˜300° C., an inert gas is used as a sputtering gas, andSiN_(x) and SiO_(x)N_(y) use Si₃N₄ and SiON targets, respectively. Whenreactive sputtering is employed, a silicon target is used and a reactivegas is injected as well as a sputtering gas of inert gas. When SiN_(x)is deposited, N₂ gas is injected. When SiO_(x)N_(y) is deposited, O₂ andN₂ gases are injected.

And, the plastic substrate is formed of a transparent material selectedfrom the group consisting of polyethersulphone (PES), polyethyleneterephthalate (PET), polycarbonate (PC), polyethylene (PE), polyethylenenaphthenate (PEN), polyolefin, polystyrene (PS), polyvinylchloride(PVC), polyester, polyamide, polynorborene (PNB), polyimide (PI),polyarylate (PAR), and the like.

The silicon based material for forming the barrier layer 30 is siliconoxynitride (SiO_(x)N_(y)) or silicon nitride (Si₃N₄ or SiN_(x)). Hence,the barrier layer 30 is formed of a single layer or multi-layers of atleast two layers which is or are selected from the insulating materials.Moreover, the silicon based insulating inorganic material, resin, andsilicon based insulating inorganic material are stacked sequentially toform the barrier layer 30.

Otherwise, the resin, silicon based insulating inorganic material, andresin are sequentially stacked to form the barrier layer 30.

And, a stacked structure of three layers including a resin layer, asilicon based insulating inorganic material layer, and a resin layer isstacked consecutively to form a plurality of the stacked structures ofthree layers including the resin, silicon based insulating inorganicmaterial, and resin layers.

And, the barrier layer 30 can be formed on a bottom of the transparentplastic substrate 20 as well as a top of the transparent plasticsubstrate 20 (not shown in the drawing).

Referring to FIG. 1 b, thermal treatment is carried out to eliminatedefects of the barrier layer 30. Since the barrier layer 30 is stackedby chemical vapor deposition, electron beam deposition, or sputteringinstead of thermal growth, a plurality of incomplete bonds betweensilicon and oxygen or nitrogen are generated. A plurality of danglingbonds generated from the incomplete bonds and porosity bring about thedefects of the barrier layer 30. Namely, the defects of the barrierlayer 30 provide the paths through which oxygen and moisture pass.

Hence, the defects should be eliminated by thermal treatment.

An annealing temperature to eliminate the defects of the barrier layer30 consisting of the silicon based compound is about 700˜1,100° C. Sinceit is unable to anneal the plastic substrate failing to be stable at theannealing temperature, local thermal treatment is carried out on asurface of the barrier layer only using an excimer laser so as not tocause damage on the substrate.

Thermal treatment of the barrier layer 30 is carried out by one of Ar₂,Kr₂, Xe₂, ArF, KrF, XeCl, and F₂ excimer lasers. Table 1 showswavelengths of the respective excimer lasers.

In this case, annealing power of the excimer laser is 10˜2,000 mJ/cm²and an ambient temperature is under 300° C. And, an instant temperatureof annealing the barrier layer 30 is at least 700° C. Besides, thenumber of the operation of annealing is at least one or more, ifnecessary.

In the above-explained annealing, one of a pulse excimer layer, acontinuous wave oscillation excimer laser, a pulse solid laser, acontinuous wave oscillation solid laser is selected to use. For example,when a silicon nitride layer (Si₃N₄ or SiN_(x)) is used for a barrierlayer, an ArF pulse excimer laser is proper for carrying out localthermal treatment on a surface of the barrier layer without causingdamage on a substrate. An absorption coefficient of the silicon nitridelayer for the ArF laser, which varies according to depositionconditions, is about 10⁵ cm⁻¹, at least 70% energy of the ArF laser isabsorbed within 2,000 Å from the surface, and a pulse width of the ArFpulse excimer laser is several tens nanoseconds.

Hence, a temperature of the surface layer is raised instantly up to atleast 700° C. without causing damage on the substrate.

After annealing, the barrier layer 30 has a highly densified homogeneouslayer 40 having a network structure consisting of silicon-oxygen orsilicon-nitrogen bonds. And, porosity and hydrogen content, which isbonded to the dangling bonds, of the highly densified homogeneous layer40 are minimized. A thickness d2 of the highly densified homogeneouslayer 40 is formed about 10˜2,000 Å thick after annealing. Since thenetwork structure is attained and the hydrogen content is reduced, thepenetration of moisture and oxygen through the transparent plasticsubstrate 20 is prevented from outside. Therefore, degradation of adisplay device using this substrate is prevented. TABLE 1 Excimer LaserWavelength Ar₂ 126 nm Kr₂ 146 nm Xe₂ 172 nm ArF 193 nm XeF 351 nm KrF250 nm XeCl 308 nm F₂ 157 nm

FIG. 2 illustrates a schematic diagram of a laser annealing systemaccording to the present invention.

Referring to FIG. 2, a process of annealing a surface of the barrierlayer 30 locally, as prepared in FIG. 1, on the transparent plasticsubstrate 20 is schematically shown. A highly densified homogeneouslayer having shield characteristics against oxygen or moisture isattained by annealing the surface of the barrier layer 30 locally byscanning the transparent plastic substrate 20 having the barrier layer30 formed thereon with an excimer laser 50. In this case, thetransparent plastic substrate 20 is put on a substrate support 55 forlaser annealing. When the plastic substrate has a dimension of 370mm×470 mm, the scanning of the excimer laser 50 is carried out forseveral minutes.

[First Embodiment]

FIG. 3 illustrates a cross-sectional view of a plastic display substrateaccording to a first embodiment of the present invention.

Referring to FIG. 3, when a barrier layer is formed on one side of atransparent plastic substrate to remove very small amount of moisture,oxygen, and the like penetrating through the transparent plasticsubstrate, a desiccant layer 25 is formed between two barrier layers 30on the transparent plastic substrate 20. In this case, the desiccantlayer 25 is formed of a metal oxide layer having excellent moistureabsorption and adsorption characteristics such as Al₂O₃, CaO, Y₂O₃, MgO,or the like and resin such as polyurea or the like to the thickness of50˜10,000 Å, and more preferably, 100˜2,000 Å.

[Second Embodiment]

FIG. 4 illustrates a cross-sectional view of a plastic display substrateaccording to a second embodiment of the present invention.

Referring to FIG. 4, when barrier layers 30 are formed respectively onboth sides, i.e. top and bottom, of a transparent plastic substrate 20to remove very small amount of moisture, oxygen, and the likepenetrating through the transparent plastic substrate, desiccant layers25 are formed between the barrier layer 30 and the top of thetransparent plastic substrate 20 and between the other barrier layer 30and the bottom of the transparent plastic substrate 20. In this case,each of the desiccant layers 25 is formed of a metal oxide layer havingexcellent moisture absorption and adsorption characteristics such asAl₂O₂, CaO, Y₂O₃, MgO, or the like and resin such as polyurea or thelike to the thickness of 50-10,000 Å, and more preferably, 100˜2,000 Å.

FIG. 5 illustrates a diagram of a bonding structure of a silicon nitridelayer as a barrier layer using a silicon based insulating material.

Referring to FIG. 5 a, since a barrier layer 30 formed of a siliconbased insulating material is stacked not by thermal growth but bychemical vapor deposition or sputtering, silicon and nitrogen fail to bebonded to each other completely. Hence, a plurality of dangling bonds 60exist and a property of the layer becomes defective. Besides, thedangling bonds 60 are bonded to hydrogen to increase the hydrogencontent in the barrier layer 30. The dangling bonds 60 and the porousproperty of the layer lead to the penetration of oxygen and moisture.

Referring to FIG. 5 b, shown is a bonding structure of a barrier layer30 after local annealing carried out on a surface of the barrier layer30 using an excimer laser. Local annealing breaks down the bond betweenthe dangling bond 60 and hydrogen at a surface of the barrier layer, anda bond 70 between silicon and nitrogen is achieved to eliminate thedangling bonds 60. The elimination of the dangling bonds 60 reduces thehydrogen content and minimizes the porosity of the barrier layer 30.Therefore, a homogeneous barrier layer enabling to prevent thepenetration of oxygen and moisture is prepared.

Moreover, in case of a single-layered layer, micro defects such aspinhole and the like on a surface of a film can be cured by carrying outat least one more overall process of barrier layer formation and laserannealing, whereby a homogeneous barrier layer can be prepared.

Moreover, in the above-explained description, sequentially stacked toform the barrier layer 30 are a silicon based inorganic material onwhich the overall process of layer formation and laser annealing iscarried out, a resin layer, and another silicon based inorganic materialon which the overall process of layer formation and laser annealing iscarried out. Or, sequentially stacked to form the barrier layer 30 are aresin layer, a silicon based inorganic material on which the overallprocess of layer formation and laser annealing is carried out, and aresin layer.

Besides, a barrier layer 30 and a highly densified homogeneous layer 40are formed on top and bottom of a plastic substrate 20, thereby enablingto maximize the preventing effect against moisture and oxygen.

The above-described method of forming the barrier layer preventing thepenetration of moisture and oxygen is not limited to the case of thetransparent plastic substrate for display but covers the case of forminga barrier layer cutting off moisture and oxygen in the air using thepurpose and method similar to the present invention.

INDUSTRIAL APPLICABILITY

The method of fabricating the plastic display substrate according to thepresent invention has the following effects or advantages.

The method according to the present invention anneals the surface of thebarrier layer locally consisting of Si—O or Si—N bonds without causingany damage on the transparent plastic substrate to form the homogeneouslayer minimizing the hydrogen content and the porosity, thereby enablingto prevent the degradation of the display device by suppressing thepenetration of external oxygen, moisture, and the like.

Moreover, multi-layers of at least 6˜7 stacked layers are required forforming the barrier layer enabling to cut off the external oxygen andmoisture by sputtering, electron beam deposition, or chemical vapordeposition according to the related art. However, the local laserannealing process of the thin barrier layer formed by the methodaccording to the present invention takes several minutes only, therebyenabling to reduce a process time as well as to minimize the number ofthe stacked layers.

Besides, in order to form the barrier layer enabling to cut off theexternal oxygen and moisture by sputtering, electron beam deposition, orchemical vapor deposition according to the related art, the thickness ofat least 2,000 Å is required. SiN_(x) has a great preventioncharacteristic against the penetration of moisture or oxygen and has ahigh surface hardness to resist a surface scratch. Yet, SiN_(x) has alow transmittance to limit the scope of application as a barrier layeron a transparent plastic substrate for display. The present inventionreduces the thickness of the SiN_(x) layer remarkably and modifies thelayer property by local annealing, thereby settling the problem oftransmittance as well as minimizing the number of the barrier layers.Therefore, the present invention enables to reduce the process time andthe product cost remarkably. Moreover, the present invention needs notto form an additional hard coating layer for the fabrication of theplastic substrate except the barrier layer to increase the surfacehardness.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention cover themodifications and variations of this invention that come within thescope of the appended claims and their equivalents.

1. A method of fabricating a plastic display substrate, comprising thesteps of: forming a silicon based barrier layer on a transparent plasticsubstrate; and annealing the barrier layer locally.
 2. The method ofclaim 1, wherein a desiccant layer is inserted between the transparentplastic substrate and the barrier layer.
 3. A method of fabricating aplastic display substrate, comprising the steps of: forming a firstsilicon based barrier layer on a transparent plastic substrate; forminga desiccant layer on the first barrier layer; forming a second barrierlayer on the desiccant layer; and annealing the first or/and secondbarrier layer locally.
 4. The method of claim 2, wherein the desiccantlayer is selected from the group consisting of Al₂O₃, CaO, Y₂O₃, MgO,and polyurea.
 5. The method of claim 1, wherein the barrier layer isselected from the group consisting of SiO_(x)N_(y) and SiN_(x) or thebarrier layer is formed of at least two complex layers.
 6. The method ofclaim 1, wherein the barrier layer is annealed using one of a pulseexcimer laser, a continuous wave oscillation excimer laser, a pulsesolid laser, and a continuous wave oscillation solid laser, an annealingpower thereof is 10˜2,000 mJ/cm², and an ambient temperature is below300° C.
 7. The method of claim 1, wherein the barrier layer is formed byat least one annealing using one of Ar₂, Kr₂, Xe₂, ArF, KrF, XeCl, andF₂ excimer lasers.
 8. The method of claim 1, wherein the barrier layeris formed to have a stacked structure of three layers comprising asilicon based insulating inorganic material, resin, and another siliconbased insulating inorganic material.
 9. The method of claim 1, whereinthe barrier layer is formed to have a plurality of stacked structureseach of which comprises three layers having a resin layer, a siliconbased insulating inorganic material, and another resin layer.
 10. Themethod of claim 3, wherein the desiccant layer is selected from thegroup consisting of Al₂O₃, CaO, Y₂O₃, MgO, and polyurea.
 11. The methodof claim 3, wherein the barrier layer is selected from the groupconsisting of SiO_(x)N_(y) and SiN_(x) or the barrier layer is formed ofat least two complex layers.
 12. The method of claim 3, wherein thebarrier layer is annealed using one of a pulse excimer laser, acontinuous wave oscillation excimer laser, a pulse solid laser, and acontinuous wave oscillation solid laser, an annealing power thereof is10˜2,000 mJ/cm², and an ambient temperature is below 300° C.
 13. Themethod of claim 3, wherein the barrier layer is formed by at least oneannealing using one of Ar₂, Kr₂, Xe₂, ArF, KrF, XeCl, and F₂ excimerlasers.
 14. The method of claim 3, wherein the barrier layer is formedto have a stacked structure of three layers comprising a silicon basedinsulating inorganic material, resin, and another silicon basedinsulating inorganic material.
 15. The method of claim 3, wherein thebarrier layer is formed to have a plurality of stacked structures eachof which comprises three layers having a resin layer, a silicon basedinsulating inorganic material, and another resin layer.